The 'What if?' game

As a child I was often accused of playing the 'what if?' game. I would try to debate philosophical or moral points by creating a hypothetical situation that would put a belief to the test. While it never worked on my parents, it can be a lot of fun. What I propose is a lively debate on how the world would be different if only one thing changed. Would stock markets crash if we could see our farts? Would ninjas rule the world if awesomeness determined how tall you were? And then the most important question: Why?

Now our legion of fan can write his/her opinion about the questions that really matter: What if...?
To get things started, here is the first what if question: What if... cows could talk?